Method and apparatus for reducing image noise

ABSTRACT

The present invention relates to an image reduction method and apparatus to be preferably used to digitize and process, for example, an image signal. Therefore, in the case of the present invention, level values a to h of peripheral pixels of a pattern  1,  the level value o of a watched pixel, and the value of a reference level θ are input and level values a to h in which absolute values for differences between level values of peripheral pixels and the watched pixel are smaller than the value of the reference level θ are output to output ports  3.  Moreover, the value of the number of output ports  3  to which level values a to h is output to an output port  4.  Moreover, the level value o of the watched pixel is supplied to a multiplier  9  and multiplied by an optional gain set value α, and the multiplication value is supplied to an adder  5  and added with the level values a to h output from the output ports  3  of a selection circuit  2  and the addition value is supplied to a divider  7.  Furthermore, the gain set value a is supplied to an adder  11  and added with a value output from the output port  4  of the selection circuit  2  and the addition value is supplied to the divider  7.  Then, a value output from the adder  5  is divided by a value output from the adder  11  and the value of the operation result is derived from an output port  8.  Thereby, the degree of signal processing is optionally set by the so-called ε-filter and the rate of watched pixels relating to the averaging operation is controlled and thereby, it is possible to optionally set the degree of signal processing and perform optimum image processing.

TECHNICAL FIELD

[0001] The present invention relates to an image noise reduction methodand apparatus for being preferably used to process, for example, animage signal by digitizing it. Particularly, the present inventionrelates to an image noise reduction method and apparatus for solving atrouble when reducing noise components of an image signal by using theso-called ε-filter.

BACKGROUND ART

[0002] For example, to reduce noise components included in an imagesignal, various methods have been proposed so far. Particularly, one ofthe simplest methods having a large noise reduction effect is a methodusing a low-pass filter (hereafter referred to as LPF). The LPF is adevice for transmitting only signals having components lower than areference frequency. That is, by inputting a signal whose frequencieschange to the LPF and observing the amplitude of an output signal, acharacteristic is obtained that a component at a higher frequency lowersin level.

[0003] However, when viewed from a different point, the LPF uses theaverage value of a watched pixel and adjacent pixels around the watchedpixel as a new value of the watched pixel. That is, in the case of thismethod, signal levels of watched pixels strongly correlated withperipheral pixels are not greatly changed in their values even if thelevels are averaged. However, random noise components having nocorrelation are averaged with noise components included in peripheralpixels and thereby, the value of the component is approached to “0”.

[0004] Therefore, when using the above LPF, the noise suppression effectincreases as the search area of peripheral pixels is widened. However,in the case of the averaging operation with peripheral pixels by theLPF, image edge information is reduced similarly to noises andresultantly, the whole image becomes blurry though noises are decreasedand a disadvantage occurs that the image quality is deteriorated.Therefore, an LPF serving as noise reduction means is not generallyused.

[0005] To solve the disadvantage of the LPF, the so-called ε-filter isdisclosed (refer to Journal of Institute of Electronics, Information,and Communication Engineers Vol. 77 No. 8, pp. 844-852, April, 1994,Kaoru Arakawa “Nonlinear Digital Filter and Its Application”). That is,in the case of the ε-filter disclosed in this document, when averaging awatched pixel and peripheral pixels, it is first determined whether theperipheral pixels has a correlation with the watched pixel.

[0006] Specifically, by setting a certain reference level θ, levels ofthe peripheral pixels are incorporated into averaging factors when thelevels are included in the range of ±θ of the level of the watched pixelbut they are not incorporated into averaging factors if they are notincluded in the range of ±θ. Thus, whether to incorporate all peripheralfactors into averaging factors is searched and a new value of thewatched pixel is obtained by the averaging operations with the watchedpixel and the peripheral pixels which are regarded as operation objects.

[0007] Therefore, even if an image edge enters a search area, when thelevels of pixels constituting the edge exceeds the range of ±θ of thelevel of the watched pixel, the edge is not regarded as an operationobject, for example, it never happens that an image becomes blurry dueto pixels constituting the edge being included in averaging. That is,with the ε-filter, it is possible to suppress only noise componentswhile leaving an image edge as it is by properly selecting the value ofhe reference level θ.

[0008] Moreover, an actual circuit configuration of the ε-filter isdescribed below by using FIG. 5. In FIG. 5, the diagram 1 shows acertain one point in an image area and imaged states of a watched pixelo and its peripheral pixels a, b, c, d, e, f, g, and h. Moreover, whensubstituting level values of these pixels with the same notation as a toh and o, the level values a to h of these peripheral pixels are suppliedto a selection circuit 2. Moreover, the value of the above referencelevel θ and the level value o of the watched pixel are input to theselection circuit 2.

[0009] In the selection circuit 2, the absolute value (|a−o|) of thedifference between the level value a of the peripheral pixel a and thelevel value o of the watched pixel o is first calculated and theabsolute value of the difference is compared with the reference level θ.Then, when the absolute value of the above difference is smaller thanthe value of the reference level θ, the level value a is output to anoutput port 3. Moreover, when the absolute value of the difference islarger than the value of the reference level θ, the level value a is notoutput to the output port 3 but the value “0” is output. Furthermore,the same calculations are applied to level values b to h of otherperipheral pixels b to h.

[0010] Therefore, eight output ports 3 equal to the number of peripheralpixels, for example, are provided for the selection circuit 2, and thelevel values a to h are output to the output ports 3 when the absolutevalue of the above difference is smaller than the value of the referencelevel θ and the value “0” is output to the ports 3 when the absolutevalue of the difference is larger than the value of the reference levelθ. Moreover, an output port 4 is provided for the selection circuit 2and a value obtained by adding “1” to the number of the output ports 3to which the above level values a to h are output is output to theoutput port 4.

[0011] That is, level values a to h are output from the output ports 3of the selection circuit 2 when absolute values of differences between awatched pixel and peripheral pixels are all smaller than the value ofthe reference level θ and the value “9” is output to the output port 4.Moreover, when absolute values of differences between the watched pixeland peripheral pixels are all larger than the value of the referencelevel θ, the value “0” is output from all output ports 3 and the value“1” is output from the output port 4.

[0012] Outputs of the output ports 3 of the selection circuit 2 and thelevel value o of the watched pixel o are supplied to an adder 5 and avalue selected by the output port 6 of the adder 5 is supplied to asubtracter 7. Moreover, a value outputted from the output port 4 of theselection circuit 2 is supplied to a divider 7. Then, in the divider 7,a value outputted from the output port 6 of the adder 5 is divided by avalue outputted from the output port 4 of the selection circuit 2 andthe value of the above operation result is output by an output port 8.

[0013] A certain reference level θ is set, and levels of the peripheralpixels are incorporated into averaging factors when the levels areincluded in the range of ±θ of the level of a watched pixel but thelevels are not incorporated into averaging factors when they are notincluded in the range and then, whether to incorporate all peripheralpixels into averaging factors is searched and only peripheral pixels tobe incorporated as averaging factors are regarded as operation objectsand as a result, a new value of a watched pixel obtained through theaveraging operation with the watched pixel is output to the output port8.

[0014] A specific circuit configuration of the selection circuit 2 ofthe above device is similar to the configuration shown in FIG. 6. Thatis, in FIG. 6, for example, eight comparators 20 equal to the number ofthe above peripheral pixels are obtained. Level values a to h of theabove peripheral pixels, the level value o of the watched pixel, and thevalue of the reference level θ are input to the comparators 20. Then,each comparator 20 outputs the value “1” when the absolute value of thedifference between a peripheral pixel and the watched pixel is smallerthan the value of the reference level θ.

[0015] Moreover, a signal output from each of the comparators 20 issupplied to an AND gate 21. Furthermore, level values a to h ofperipheral pixels are supplied to the AND gate 21 and corresponding oneof the level values a to h of peripheral pixels is output to the outputports 3 through the AND gate 21 when a signal output from each of theabove comparators 20 is equal to “1”. Furthermore, signals output fromthe comparators 20 are supplied to an adder 22. Furthermore, an additionoutput of the adder 22 is supplied to an adder 23 and the value “1” isadded and output to the output port 4.

[0016] Thereby, in the case of this circuit configuration, level valuesa to h of peripheral pixels are output through the AND gate 21 whenabsolute values of differences between level values a to h and the levelvalue o of the watched pixel are smaller than the value of the referencelevel θ. Moreover, the value “0” is output when absolute values of thedifferences are larger than the value of the reference level θ.Furthermore, a value obtained by adding “1” to the number of levelvalues a to h output to the output ports 3 through the above AND gate 21is output to the output port 4.

[0017] Thus, the selection circuit 2 outputs level values a to h whenabsolute values of the above differences are smaller than the value ofthe reference level θ and a value obtained by adding “1” to the numberof output level values a to h. Moreover, the level values a to h and thelevel value o of the watched pixel are added and the addition value isdivided by a value obtained by adding “1” to the number of output levelvalues a to h. Thereby, the averaging operation is applied to onlypixels regarded as averaging factors and a new value of the watchedpixel is derived.

[0018] Thus, in the case of the above ε-filter, it is possible toeffectively reduce noises while preserving an image edges. However, evenwhen using the ε-filter, because basic processing is performed by anLPF, image details having a high-frequency component and a smallamplitude disappear. Meanwhile, when an object is flat, noises easilybecome conspicuous and the ε-filter has a large effect. However, whenthere are many high-frequency components, the effect of the ε-filter issmall and noises do not easily become conspicuous.

[0019] Therefore, when an object has many high-frequency components, theε-filter is turned off. However, it is alternative whether to performsignal processing by the ε-filter or not. In this case, a case occursthat a state in which processing is performed or not performed is notnecessarily the optimum image processing. That is, noises increase whenno operation is performed or image details disappear when an operationis performed depending on the content of an object.

DISCLOSURE OF THE INVENTION

[0020] The present invention makes it possible to optionally set thedegree of signal processing by controlling the rate of watched pixelsrelating to the averaging operation by the so-called ε-filter.Therefore, in the case of the present invention, the averaging operationis performed by weighting level values of watched pixels and optionallycontrolling the rate of the weighting. Image noise reduction method andapparatus of the present invention are disclosed correspondingly to theabove mentioned.

BRIEF DESCRIPTION OF DRAWINGS

[0021]FIG. 1 is a block diagram showing a configuration of an embodimentof a selection circuit used for image noise reduction method andapparatus to which the present invention is applied.

[0022]FIG. 2 is a block diagram showing a configuration of anotherembodiment of a selection circuit used for image noise reduction methodand apparatus to which the present invention is applied.

[0023]FIG. 3 is a block diagram for explaining an essential portion ofthe configuration in FIG. 2.

[0024]FIG. 4 is illustration for explaining operations of theconfiguration in FIG. 2.

[0025]FIG. 5 is a block diagram for explaining a conventional imagenoise reduction apparatus.

[0026]FIG. 6 is a block diagram showing a configuration of a selectioncircuit used for conventional image noise reduction method andapparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

[0027] The present invention is described below by referring to theaccompanying drawings. FIG. 1 is a block diagram showing a configurationof an image noise reduction apparatus to which image noise reductionmethod and apparatus of the present invention are applied. In FIG. 1, aportion corresponding to that in FIG. 5 is provided with the samesymbol.

[0028] In FIG. 1, a pattern 1 shows a certain point in an image area thesame as FIG. 5, which images states of a watched pixel o and itsperipheral pixels a, b, c, d, e, f, g, and h. Moreover, whensubstituting level values of these pixels with the same notations assymbols a to h and o, the level values a to h of these peripheral pixelsare supplied to the selection circuit 2. Furthermore, the value of theabove reference level θ and the level value o of the watched pixel areinput to the selection circuit 2.

[0029] In the selection circuit 2, the absolute value (|a−o|) of thedifference between the level value a of the peripheral pixel a and thelevel value o of the watched pixel o is first computed and the absolutevalue for the difference is compared with the reference level θ. Then,when the absolute value of the above difference is smaller than thevalue of the reference level θ, the level value a is output to theoutput ports 3. When the absolute value of the difference is larger thanthe value of the reference level θ, the level value a is not output tothe output ports 3 but the value “0” is output. The same operation isfurther applied to level values b to h of other peripheral pixels b toh.

[0030] Therefore, for example, eight output ports 3 equal to the numberof peripheral pixels are provided to the selection circuit 2, and thelevel values a to h are output to these output ports 3 when the absolutevalue of the above difference is smaller than the value of the referencelevel θ and the value “0” is output to the output ports 3 when theabsolute value of the difference is larger than the value of thereference level θ. Moreover, an output port 4 is provided to theselection circuit 2 and the value of the number of the output ports 3 towhich the above level values a to h are output is output to the outputport 4. This point is different from the case of FIG. 5.

[0031] That is, when absolute values of differences between a watchedpixel and peripheral pixels are all smaller than the value of thereference level θ, the level values a to h are output to the outputports 3 and the value “8” is output to the output port 4. Moreover, whenabsolute values of differences between the watched pixel and peripheralpixels are all larger than the value of the reference level θ, the value“0” is output from all the output ports 3 and the value “0” is output tothe output port 4.

[0032] Furthermore, the level value o of the above watched pixel issupplied to a multiplier 9 and an optional gain set value α is suppliedto the multiplier 9 and the multiplication of (α×o) is executed. Then,the multiplication value “α×o” derived from the output port 10 of themultiplier 9 is supplied to the adder 5 and added with the level valuesa to h selected by the output ports 3 of the above selection circuit 2.Moreover, an addition value derived from the output port 6 of the adder5 is supplied to a divider 7.

[0033] Furthermore, the above gain set value a is supplied to an adder11 and added with a value output from the output port 4 of the selectioncircuit 2. Then, the addition value of the gain set value a and thevalue of the number of output ports 3 to which the level values a to hare output, which is obtained by the output port 12 of the adder 11, issupplied to the divider 7. Thus, in the divider 7, a value output fromthe output port 6 of the adder 5 is divided by a value output from theoutput port 12 of the adder 11 and the value of the operation result isderived from the output port 8.

[0034] Thereby, when a gain set value α is equal to, for example, 1, theconventional averaging operation is performed and a new value of awatched pixel obtained through the averaging operation is derived fromthe output port 8. However, when assuming a gain set value α as, forexample, 8, the rate of watched pixels relating to the averagingoperation increases, the change of new values of watched pixels derivedfrom the output port 8 is decreased, and a new value close to theoriginal value is derived.

[0035] That is, when absolute values of differences between a watchedpixel and peripheral pixels are all smaller than the value of thereference level θ, the value [a+b+c+d+e+f+g+h+α×o] is derived from theoutput port 6 of the adder 5. Moreover, the value [8+α] is derived fromthe output port 12 of the adder 11. Then, in the divider 7,(a+b+c+d+e+f+g+h+α×o)/(8+α) is computed and derived from the output port8.

[0036] Then, for example, when absolute values of differences between awatched pixel and peripheral pixels are all smaller than the value ofthe reference level θ and a gain set value α is assumed as 1, a newvalue of (α+b+c+d+e+f+g+h+o)/(8+1) is derived from the output port 8. Inthis case, the rate of peripheral pixels and a watched pixel in the newvalue is 1/9=11.1% of the whole and thereby, image detail componentsbecome 1/9.

[0037] When absolute values of differences between a watched pixel andperipheral pixels are all smaller than the value of the reference levelθ and a gain set value α as 8, a new value of(a+b+c+d+e+f+g+h+8×o)/(8+8) is derived from the output port 8. In thiscase, the rate of peripheral pixels in the new value is 1/16=6.25% whilethe rate of watched pixels is 8/16=50% of the whole.

[0038] That is, in this case, by setting a gain set value to 8, the rateof a watched pixel is increased and the noise reduction effect islowered by a value equivalent to the increased rate but image detailcomponents are preserved. Thus, by optionally setting a gain set value αin the above circuit, it is possible to optionally set the degree ofsignal processing by controlling the rate of a watched pixel relating tothe averaging operation in the so-called ε-filter and thereby, optimumimage processing can be executed.

[0039] Therefore, for example, a photographer determines the state of anobjet and sets a gain set value α to an optional value so that optimumimage processing can be performed. Specifically, a gain set value α isset to 1 in the case of a flat object such as a beach or sand hill and 8in the case of a varied object such as a street corner. When aphotographer actually manually sets a gain set value α, it is proper toset it to one of two stages such as 1 or 8.

[0040] However, even when the above setting is performed, the operationof an ε-filter is continued. Therefore, even if a gain set value α isset to 8, noises are reduced though the effect is deteriorated. Thispoint is greatly different from the case of the above conventionalε-filter in which whether to perform signal processing or not isalternatively selected. Moreover, when setting includes no signalprocessing performed by an ε-filter, it is possible to apply a propersignal processing to various types of objects.

[0041] Therefore, in the case of the above embodiment, because theaveraging operation is performed by weighting level values of watchedpixels and optionally controlling the rate of the weighting levelvalues, it is possible to optionally set the degree of signal processingby controlling the rate of watched pixels relating to the averagingoperation in the so-called ε-filter and thereby, perform optimum imageprocessing.

[0042] Consequently, according to the present invention it is possibleto solve the following problem with a conventional apparatus in whichwhether or not to perform the signal processing in the so-calledε-filter has been an alternative, though in that case the state in whichsignal processing is performed or the state in which signal processingis not performed is not necessarily said to be an optimum imageprocessing, either.

[0043] In the case of the above embodiment, a photographer determinesthe state of an object and manually sets a gain set value α. However, itis also possible to automatically set a gain set value α by determiningthe image of an object through image processing or the like. Anembodiment making it possible to automatically set a gain set value α isdescribed below.

[0044] That is, in this case, the level values a to h of peripheralpixels and the level value o of a watched pixel are supplied to anα-computing section 13 as shown in FIG. 2. In the α-computing section13, the spatial frequency of an image formed by the above watched pixeland peripheral pixels is determined by the α-computing section 13 andmoreover, a gain set value α is computed by determining the distributionof the spatial frequencies. Then, the gain set value α computed by theα-computing section 13 is supplied to the above multiplier 10 and adder11. Other portions are constituted the same as the case of FIG. 1.

[0045] Furthermore, a specific configuration of the above α-computingsection 13 is described below by referring to FIG. 3. However,embodiments of the present invention are not limited to thisconfiguration. In FIG. 3, level values of the above peripheral pixels ato h and the watched pixel o are supplied to a spatial high-pass filter(HPF) 100. The high-pass filter 100 detects two-dimensionally how manyhigh-frequency components are pre sent in an area when assuming the tapcoefficient of the watched pixel as the value “8” and the tapcoefficients of the peripheral pixels a to h as the value “−1”.

[0046] Then, a signal obtained from the output port 101 of the high-passfilter 100 is supplied to a conversion-to-absolute-value circuit 102 anda signal obtained from the output port 103 of theconversion-to-absolute-value circuit 102 is supplied to a low-passfilter (LPF) 104. Moreover, a signal obtained from the output port 105of the low-pass filter 104 is supplied to a comparator 106, and iscompared with a reference value optionally set (Reg), and a comparisonoutput is supplied to a control terminal of a selector 107.

[0047] Thereby, in the selector 107, when the number of high-frequencycomponents which are spatial frequency components of the peripheralpixels a to h and the watched pixel o increases, the comparison outputof the comparator 106 becomes “H” and a gain set value α1=8 is selected.However, when the number of high-frequency components which are spatialfrequency components of the peripheral pixels a to h and the watchedpixel o decreases, the comparison output of the comparator 106 becomes“L” and a gain set value α2=1 is selected. Then, a selected gain setvalue α is derived from the α-computing section 13.

[0048] That is, when, for example, the signal shown in FIG. 4A is input,an output of the high-pass filter 100 shows the waveform shown in FIG.4B and an output of the conversion-to-absolute-value circuit 102obtained by converting the signal into an absolute value shows thewaveform shown in FIG. 4C. In this case, at the portion of an inputsignal where the signal changes are moderate at the left of FIG. 4C, anoutput of the conversion-to-absolute-value circuit 102 becomes low-leveland at the portion on the right side of FIG. 4C where input signalchanges are violent, an output of the conversion-to-absolute valuebecomes high level.

[0049] Then, these signals are sent to the low pass filter 104 to derivea signal indicating an envelope curve of the whole level values shown inFIG. 4D, and by comparing the signal by the comparator 106 with thepreset reference value (Reg) it is possible to form a selection signalfor selecting, for example, a gain set value α1 =8 or a gain set valueα2=1 by the selector 107 in accordance with the degree of changes in theinput signal. Thereby, a selected gain set value α is derived from thea-computing section 13.

[0050] Therefore, according to this embodiment, a gain set value α isautomatically set and it is possible to eliminate the complexity that aphotographer manually sets the value α. Moreover, according to thisembodiment, it is possible to always change a gain set value α inaccordance with states of the peripheral pixels a to h and the watchedpixel o. For example, it is possible to set an optimum gain set value afor each portion of an individual object by detecting the portion in onescreen.

[0051] Moreover, in the above embodiment, a gain set value a is set totwo stages such as the gain set value α1=8 or the gain set value α2=1.However, it is also possible to set a gain set value α in multiplestages by more minutely analyzing the rate of high-frequency componentsin spatial frequency components of the peripheral pixels a to h and thewatched pixel o. Furthermore, though not illustrated, it is possible tocontrol whether or not to perform signal processing by an ε-filter bycontrolling the selection circuit 2 in accordance with a signal outputfrom the α-computing section 13.

[0052] Thus, the above image noise reduction method is an image noisereduction method of detecting level differences between a watched pixeland its peripheral pixels, selecting only pixels whose level differencesare smaller than a reference value, and applying the averaging operationto them, in which the degree of signal processing can be optionally setby weighting the level values of watched pixels and optionallycontrolling the rate of weighting level values and performing theaveraging operation and thereby controlling the rate of watched pixelsrelating to the averaging operation by the so-called ε-filter andthereby, optimum image processing can be performed.

[0053] Moreover, the above image noise reduction apparatus is an imagenoise reduction apparatus for reducing noise components, which comprisesdetection means for detecting level differences between a watched pixeland its peripheral pixels, selection means for selecting only pixelswhose level differences are smaller than a reference value, andoperation means for performing the averaging operation by using selectedpixels and which makes it possible to optionally set the degree ofsignal processing by using a means for weighting level values of watchedpixels, controlling the rate of the weighting level values, andperforming the averaging operations by the operation means and therebycontrolling the rate of watched pixels relating the averaging operationsby the so-called ε-filter and thereby, optimum image processing can beperformed.

[0054] The present invention is not restricted to the above embodimentsbut it allows various modifications as long as the modifications are notdeviated from the spirit of the present invention.

[0055] That is, according to the present invention, it is possible tooptionally set the degree of signal processing by weighting level valuesof watched pixels, controlling the rate of the weighting level values,performing the averaging operations, and thereby controlling the rate ofwatched pixels relating to the averaging operations by the so-calledε-filter.

[0056] Moreover, according to the present invention, it is possible toperform optimum image processing in accordance with the image of anobject by controlling weighting in accordance with the image of theobject.

[0057] Furthermore, according to the present invention, it is possibleto eliminate the complexity that a photographer manually sets a gainbecause the gain is automatically set by determining the spatialfrequency of an image formed by a watched pixel and its peripheralpixels and controlling weighting in accordance with the abovedetermination result.

[0058] Furthermore, according to the present invention, it is possibleto perform very preferable processing by digitizing and processing eachpixel level.

[0059] Furthermore, according to the present invention, it is possibleto optionally set the degree of signal processing by weighting levelvalues of watched pixels, optionally controlling the rate of theweighting level values, performing the averaging operations, therebycontrolling the rate of watched pixels relating to the averagingoperations by the so-called ε-filter and thereby, optimum imageprocessing can be performed.

[0060] Furthermore, according to the present invention, it is possibleto perform optimum image processing in accordance with the image of anobject by using a means for controlling weighting in accordance with theimage of the object.

[0061] Furthermore, according to the present invention, it is possibleto eliminate the complexity that a photographer manually sets a gainbecause the gain is automatically set by using means for determining thespatial frequency of an image formed by a watched pixel and itsperipheral pixels and control means for controlling weighting inaccordance with the above determination result.

[0062] Furthermore, according to the present invention, it is possibleto perform very preferable processing by digitizing and processing eachpixel level.

[0063] Thereby, a conventional apparatus alternatively selects whetheror not to perform signal processing by the so-called ε-filter. In thiscase, a case occurs in which a state performing or not performingprocessing is not necessarily the optimum image processing. However, thepresent invention can preferably solve the problems.

DESCRIPTION OF REFERENCE NUMERALS

[0064]1 . . . PATTERN SHOWING A CERTAIN POINT OF IMAGE AREA,

[0065]2 . . . SELECTION CIRCUIT

[0066]4, 6, 8, 10, 12 . . . OUTPUT PORT,

[0067]5, 11 . . . ADDER

[0068]7 . . . DIVIDER

[0069]9. . . MULTIPLIER

[0070]13 . . . α-COMPUTING SECTION

[0071]100 . . . SPATIAL HIGH-PASS FILTER (HPF)

[0072]101, 103, 105 . . . OUTPUT PORT

[0073]102 . . . CONVERSION-TO-ABSOLUTE-VALUE CIRCUIT

[0074]104 . . . LOW-PASS FILTER (LPF)

[0075]106 . . . COMPARATOR

[0076]107 . . . SELECTOR

1. An image noise reduction method for reducing a noise component bydetecting level differences between a watched pixel and peripheralpixels, selecting only pixels said level differences of which aresmaller than a reference value to thereby perform averaging operations,characterized by weighting the level values of said watched pixel aswell as optionally controlling the rate of said weighting to performsaid averaging operations.
 2. An image noise reduction method accordingto claim 1, characterized by controlling the weighting in accordancewith the image of an object.
 3. An image noise reduction methodaccording to claim 1, characterized by determining the spatial frequencyof an image comprised of the watched pixels and peripheral pixels andcontrolling the weighting in accordance with the above determinationresult.
 4. An image noise reduction method according to claim 1,characterized by digitizing and processing each of the pixel levels. 5.An image noise reduction apparatus for reducing a noise component,comprising: detection means for detecting level differences between awatched pixel and peripheral pixels; selection means for selecting onlypixels said level differences of which are smaller than a referencevalue; and operation means for performing averaging operations by usingsaid selected pixels; characterized by providing a means for weightinglevel values of said watched pixel as well as optionally controlling therate of said weighting to perform the averaging operations by theoperation means.
 6. An image noise reduction apparatus according toclaim 5, characterized by including control means for controlling theweighting in accordance with the image of an object.
 7. An image noisereduction apparatus according to claim 5, characterized by including ameans for determining the spatial frequency of an image comprised ofsaid watched pixels and peripheral pixels and control means forcontrolling the weighting in accordance with the above determinationresult.
 8. An image noise reduction apparatus according to claim 5,characterized by digitizing and processing each of said pixel levels.